Polybenzoxazole film



United States Patent Office Patented June 10, 1969 U.S. Cl. 260-47 1 Claim ABSTRACT OF THE DISCLOSURE Film of polybenzoxazole which is creasable.

This application is a division of our copending application Ser. No. 288,534, filed June 17, 1963, now US. Patent No. 3,332,907.

This invention relates to novel shapeable or tractable polymeric compositions and, more particularly, to the preparation of the tractable polymeric compositions, their formation into shaped articles, and their conversion into substantially intractable polymeric articles. As used in the present specification, shapeable refers to the ability of the polymeric compositions to be shaped into useful structures by extrusion through dies, casting as films, coating on substrates, or by similar processing.

The outstanding physical and chemical properties of certain polymers make them extremely useful in the form of shaped structures such as films, filaments, tubing, etc. However, the same outstanding physical and chemical properties make it extremely difiicult to shape these polymers into useful structures. One purpose of the present invention is to provide a group of polymeric compositions having satisfactory physical and chemical properties, but which can easily be formed into shaped structures. A further purpose is to select polymeric compositions which, in the form of shaped structures, can be converted into polymers having even more outstanding physical and chemical properties.

Specifically, the object of the present invention is to provide shapeable compositions of certain substituted polyamides. A further object is to provide shaped structures of these polyamide compositions. A still further object of the invention is to convert the polyamide structures to structures of polymers having even more desirable properties than the polyamides, e.g., structures of polybenzoxazoles. Other objects will appear hereinafter.

The objects are accomplished by a composition containing at least one polyamide having the following structural formula:

O H H wherein R is an aromatic tetravalent radical; R is arylene; X is selected from the group consisting of hydrog r R2:

R being lower alkyl (up to six carbon atoms); and R R and R each being selected from the group consisting of hydrogen and R X being preferably hydrogen and R and wherein n is an integer sufiicient to provide a film-forming polyamide, i.e., having an inherent viscosity of at least 0.3, preferably 05-50, as measured at 30 C.

as a 0.5% solution in a suitable solvent, concentrated sulfuric acid.

The polyamides for use in the composition of the present invention are solids with an undefined melting point. Their infrared absorption spectra are characterized by absorption bands at ca. 3.1 microns due to the N-H bond of the amide groups and at ca. 6.0 microns due to the C O bond of the amide groups.

The process for preparing the polyamide compositions comprises reacting by mixing at least one organic diamine having the structural formula:

I HaNIItNHI wherein R is an aromatic tetravalent radical each amino group of said diamine attached directly to a carbon atom of a ring of said aromatic radical ortho or peri to the carbon atom to which an OX is directly attached; with at least one halide-substituted dicarboxylic acid, or an anhydride of the dicarboxylic acid, or lower alkyl esters of the dicarboxylic acid, or phenyl esters of the dicarboxylic acid, preferably the halide-substituted dicarboxylic acid having the structural formula:

wherein R is arylene; and Y is halogen, preferably chlorine, in an organic solvent for at least one reactant, said solvent being inert to the reactants, for a time, preferably of at least 1 minute, and at a temperature below 275 C., sutficient to provide the corresponding polyamide.

It should be understood that one purpose of the process is to provide a composition that can be shaped into useful objects. In determining .a specific time and a specific temperature for forming the polyamide of a specified diamine and a specified substituted acid, several factors must be considered. The maximum permissible temperature will depend on the diamine used, the acid used, the particular solvent, the percentage of polyamide desired in the final composition and the minimum period of time that one desires for the reaction. Temperatures up to 275 C. may be tolerated to provide shapeable compositions of the polyamide. The particular temperature below 275 C. that must not be exceeded for any particular combination of diamine, diacid-halide, solvent and reaction time to provide a reaction product composed of the shapeable polyamide will vary but can be determined by a simple test by any person of ordinary skill in the art.

The resulting polymeric hydroxy or alkoxy amide or the like can be cast or extruded into a film, filament, rod tube or other desired shape, or it can be used in solution as a coating composition. After shaping the composition composed predominantly of the polyamide, preferably still in the solvent, into a useful article, e.g., filament film, tube, rod, etc., and drying the article, it is preferred to convert the polyamide to another polymer to modify the properties of the shaped structure. Thus, the polyamide is converted to the corresponding polybenzoxazole by treatment to split out the elements of XOH, i.e., by heating at about 275-475" 0., preferably 330-450 C. for a suflicient time, usually at least one hour, to effect such conversion.

The polybenzoxazoles of this invention find many applications in a wide variety of physical shapes and forms. Among the most significant of these forms are films and fibers. Films and fibers of this polymer not only possess excellent physical properties at room temperature, but retain their strength at elevated temperatures for prolonged periods of time. Because of the solubility of the polymer precursors, they can be processed into shaped articles such as films, fibers, tubes, rods, sheets and disc by conventional technique, and then converted into the final high-melting, relatively intractable cyclized polymers, the polybenzoxazoles.

The final shaped article may consist of the heterocyclic polymer alone or as a blend with other polymers and/or modified with inert materials. Depending on their nature, the inert materials may be added before or after shaping. For example, fillers such as pigments, electrically conductive carbon black and metal particles, abrasives, dielectrics and lubricating polymers may be added conveniently to the intermediate polymer as such or to a solution of the intermediate polymer before shaping. Certain abrasives and electrically conductive materials are better added as surface layers. A cellular form or foam of the final polymer may be produced by adding a conventional blowing agent to the intermediate polymer, either alone or in combination with a filler, followed by heating to decompose the agent and cyclize the polymer units. Alternatively, cellular products can be made by dispersing bubbles (of air, carbon dioxide, nitrogen, etc.) into a melt or solution of the intermediate polymer before shaping and cyclization.

Instead of being shaped itself, the intermediate polymer can be used as a coating composition. Sometimes a melt of this polymer is suitable, but a solution generally is more useful. The liquid coating composition containing the polymer, either alone or modified by the addition of fillers and/or foaming agents, may be applied by any of the usual techniques (doctoring, rolling, dipping, brushing, spraying) to a great variety of substrates. Such substrates include copper, brass, aluminum, steel, and other metals in the form of sheets, fibers, wires, screening; mineral structures such as asbestos; glass in the form of sheets, fibers, foams, fabrics, etc.; polymeric material such as cellulosic materials (cellophane, wood, paper, etc.); polyolefiris (polyethylene, polypropylene, polystyrene, etc.), polyesters (polyethylene terephethalate, etc.) polyamides, polyimides, perfiuorocarbon polymers (polytetrafluoroethylene, copolymers of tetrafluoroethylene with hexafiuoropropylene, etc.), polyurethanes, in the form of sheets, fibers, foams, woven and non-woven fabrics, screening, etc.; leather sheets; etc. The polymeric substrates can be metallized before coating, or treated with a conventional adhesive or other agent to improve surface receptivity. Films of the final cyclized polymer can be laminated to any of the above substrates, often with the aid of a commercially available adhesive.

Films formed from the polymer of this invention may be used wherever films have heretofore been used. They serve advantageously in wrapping, packaging and bundling applications. Additionally, the film-forming polymer may be used in automobile and aviation interior head lining materials, decorative trim, high tempearture electrical insulation, in the form of corrosion-resistant pipe, duct work, containers and container linings, and the laminating structures mentioned previously. In fiber form, the polymer of the present invention offers possibilities for high temperature electrical insulation, protective clothing and curtains, filtration media, packing and gusseting materials, brake linings and clutch facings.

In the preparation of the shapeable compositions and the final polymer of the present invention it is essential that the molecular weight be such that the inherent viscosity of the polymers be at least 0.3, preferably 0.5-5.0. The inherent vsicosity is measured at 30 C. at a concentration of 0.5% by weight of the polymer in a suitable solvent. The suitable solvent for the purpose of the present invention has been chosen as concentrated sulfric acid. The viscosity of the polymer solution is measured relative to that of the'solvent alone and the viscosity of solution viscosity of solvent natural logarithm inherent viscosity mer art, inherent viscosity is directly related to the molecular weight of the polymer.

The starting materials for forming the products of the present invention are at least one compound of the class: ar'omatic diacid halides, aromatic diacid anhydrides and aromatic diacid lower alkyl or phenyl esters and at least one compound of the class: bis(o-hydroxy)arylene diamines, bis(o-lower alkoxy) arylene diamines and similar diamines.

The most readily available diamine is 3,3'-dihydroxybenzidine. This diamine may be obtained by demethylation of commercially available o-dianisidine with aluminum chloride according to the procedure described in US. Patent 2,497,248. Also operable and prepared similarly are other bis (ortho hydroxy amine phenyl) compounds and their derivatives of the structure.

OX OX where Y is any one of the following: carbon-carbon bond linking the two aromatic rings; a divalent hydrocarbon radical, i.e., alkylene or alkylidene; a divalent perhalocarbon radical, i.e., perfluoroalkylene or alkylidene, oxygen; sulfur; SO; CO CONH; COO;

where R is hydrogen or lower alkyl.

.From the standpoint of availability, the preferred species is that in which Y is a carbon-to-carbon bond. Examples of those having alkylene bridges are the members in which Y is CH and CHa The linkage is preferably para to either the amino or hydroxy group. Representative operable diamines are: bis( 3-hydroxy-4-amino biphenyl;

bis( 3-methoxy-4-amino biphenyl;

- 1,2-bis(3-hydroxy-4-aminophenyl)ethane;

2,-Z -bis 3-hydroXy-4-aminophenyl propane;

bis( 3-hydroxy-4-aminophenyl bis (trifiuoromethyl) methane;

bis 3-hydroxy-4-aminophenyl) ether;

bis( 3-hydroxy-4-aminophenyl (sulfide;

bis 3-hydroxy-4-aminophenyl) sulfone;

bis( 3 -hydroxy-4-aminophenyl )ketone bis 3-hydroxy-4-aminophenyl methane;

-N-. (3-hydroxy-4-aminophenyl -3-hydroxy-4-aminobenzamide;

(3 hydroxy-4-aminophenyl) -3-hydroxy-4-amin obenzoate;

( 3-hydroxy-4-aminophenyl) -3-hydroxy-4-aminophenyl carbamate;

N,N-bis 3 hydroxy-4-aminophenyl urea;

bis (3-amino-4-hydroxyphenyl ether;

bis( 3-amino-4-hydroxyphenyl sulfide;

bis 3-amino-4-hydroxyphenyl sulfone;

bis( 3-amino-4-hydroxyphenyl sulfoxide;

bis 3-amino-4-hydroxyphenyl ketone;

bis 3-amino-4-hydrovyphenyl methane;

1,2-bis 3-amino-4-hydroxyphenyl ethane;

2,2-bis( 3-amino-4-hydroxyphenyl) propane;

bis 3-amino-4-hydroxyphenyl) dimethyl silane bis(3-amino-4-hydroxyphenyl) dibutyl silane;

bis 3-amino-4-hydroxyphenyl methyl phosphine;

bis(3-amino-4-hydroxyphenyl (butyl phosphine;

l,5-diamino-2,6-naphthalene diol;

1,o diamino-2,5-naphthalene diol;

2,5 -diamino-1,6-naphthalene diol;

2,6-diamino-l,S-naphthalene diol;

1,6-diamino-2,7-dihydroxy naphthalene; 2,5-diamino-1,7-dihydroxy naphthalene; l,7-diamino-2, 6-dihydroxy naphthalene; 2,7-diamino-l,6-dihydroxy naphthalene; 2,7-diamino-3,6-dihydroxynaphthalene1 3,7-diamino-2,6-dihydroxynaphthalene; 1,5-diamino-4,S-dihydroxynaphthalene; l,5-diamino-2,6-dihydroxy anthracene; 1,8-diamino-2,7-dihydroxy phenanthrene; 1,4-diamino-2,5-dihydroxy benzene; l,3-diamino-4,6-dihydroxy benzene; bis (3-acetoXy-4-amino)biphenyl; bis(3-thionoacetoxy-4-amino)biphenyl;

methyl carbonate ester of Representative of the radicals provided by the diamines just disclosed are H and where Y is as defined hereinbefore.

Representative members of the class of derivatives of aromatic dicarboxylic acids which are useful in the invention are:

isophthaloyl chloride;

isophthaloyl bromide;

terephthaloyl chloride;

terephthaloyl bromide; biphenyl-3,3'-dicarbonyl chloride; biphenyl-3,3'-dicarbonyl bromide; biphenyl-4,4'-dicarbonyl chloride; biphenyl-4,4-dicarbonyl bromide;

bis 3-chlorocarbonylphenyl methane; bis(d -chlorocarbonylphenyl)methane; 2,2-bis (3-chlorocarbonylphenyl) propane; 2,2-bis(4-chlorocarbonylphenyl)propane; naphthalene-'2,6-dicarbonyl chloride; bis(3-chlorocarbonylphenyl)etherj bis(4-chlorocarbonylphenyl)ether;

bis 3chlorocarbonylphenyl sulfide;

bis (4-chloroc arb onylphenyl) sulfide; bis(3-chlorocarbonylphenyl) sulfone; and his (4-chlorocarb onylphenyl) sulfone.

Representative radicals provided by this class include a an u as where Z is selected from the group consisting of alkylene of l to 3 carbon atoms, oxygen, sulfur, and SO Also operable are the lower alkyl or aryl esters of the foregoing aromatic acids as well as their anhydrides with fatty acids such as acetic acid and alpha-halogenated fatty acids such as trifluoroacetic acid, trichloroacetic acid, difluoroacetic acid and dichloroacetic acid.

As mentioned previously, the reaction of any of these aromatic carboxylic acid derivatives with the hydroxy amines and their derivatives may be carried out in an inert solvent to form the polymeric hydroxy or alkoxy amide or the like. This polymeric intermediate can be shaped and after it is in the desired shape, converted into the corresponding polybenzoxazole by heating at a temperature above about 275 C. This conversion can be started if desired in a high boiling solvent such as diphenyhnethane, and then finished by vigorous heating of the dry polymer. The reaction is aided by a current of inert gas such as nitrogen, or by operating in a vacuum, both of which help to remove the by-product water or alcohol. The structural formula of the resulting polybenzoxazole follows:

wherein R is an aromatic tetravalent radical; each nitrogen atom being attached directly to a carbon atom of a ring of said aromatic radical and being ortho or peri to the oxygen atom; R is arylene; and n. is an integar sufficiently high to provide a film-forming polymer.

The solvents useful in the solution polymerization process for synthesizing the polyamide compositions of the present invention are the organic solvents whose functional groups do not react with either of the reactants to a greater extent than the reactants do with each other. Besides being inert to the system and, preferably, being a solvent for the product, the organic solvent must be a solvent for at least one of the reactants, preferably for both of the reactants. The normally liquid organic solvents of the N,N-dialkylcarboxylamide class are useful as solvents in the process of this invention. The preferred solvents are the lower molecular weight members of this class, particularly N,N-dimethylformamide and N,N-dimet-hylacetamide. They may easily be removed from the polyamide-acid and/ or polyamide-acidshaped articles by evaporation, displacement or diffusion. Other typical compounds of this useful class of solvents are: N ,N-diethylformamide, N,N-diethylacetamide, N,N-dimethylmethoxy acetamide, N methyl caprolactam, etc. Other solvents which may be used in the present invention are: dimethylsulfoxide, N-methyl-Z-pyrrolidone, tetramethylene urea, pyridine, dimethylsulfone, hexamethylphosphoramide, tetramethylene sulfone, forma'mide, N-methylformamide and N-acetyl-Z-pyrrolidone. The solvents can be used alone, in combination of solvents, or in combination with poor solvents such as benzene, benzonitrile, dioxane, butyrolactone, xylene, toluene and cyclohexane.

This invention will be more clearly understood by referring to the examples which follow. These examples, which illustrate specific embodiments of the present invention, should not be construed to limit the invention in any way.

7 EXAMPLE 1 A 0.2 g. sample of the polyamide from 3,3'-dimethoxybenzidine and isophthaloyl chloride, the polymer having an inherent viscosity of 2.0 at 0.5% in concentrated sulfuric acid at 30 C., in N,N-dimethylacetamide is cast as a film and then heated at 400430 C. at less than 0.1 mm. pressure for 4 hours. After cooling, the amber solid product is found to be completely insoluble in N,N-dimethylacetamide, in contrast to the original polyamide which is quite soluble. From this and infrared scans it is concluded that the polyamide has been converted to the desired polybenzoxazole.

EXAMPLE 2 A 10.8 g. portion of 3.3-dihydroxybenzidine (0.05 mole) is dissolved in 40 ml. of dry N,N-dimethylacetamide under an atmosphere of dry nitrogen. To this is added with stirring 10.15 g. (0.05 mole) of pure isophthaloyl chloride. The solution becomes greenish and quite viscous. Twenty ml. of N,N-dimethylaceta;mide is used to wash in the last traces of the acid chloride. The mixture is stirred for 25 minutes at room temperature, whereupon it becomes so viscous that further stirring is impossible. The reaction mixture is rapidly extracted three times with 400 ml. portions of 5% sodium bicarbonate solution in a Waring Blendor, then three times each with Water, 2B alcohol and dry ether, and then dried for 12 hours at C. at less than 1 mm. pressure. The product is a green powder which is swelled, but not completely dissolved, by N,N-dimethylacetamide or N methyl pyrrolidone. The product has an inherent viscosity of 2.3 at 0.5% in concentrated H 50 at C. Its polyamide structure is confirmed by infrared examination.

A mixture of 5 g. of the powdered poly(hydroxyamide) prepared as described above and 95 g. of hexamethylphosphoramide is stirred at 60 C. for 30 minutes, then cooled and filtered through a 200 mesh screen. The solution is degassed by centrifuging and cast on :Pyrex glass plates into 15-20 mil layers which are evaporated in a forced draft oven at 120 C. for 30-45 minutes. The partially dried films are then stripped from the glass, clamped to frames and vacuum dried at 100-120" -C. The resulting films are yellow, tough and creasable.

One of these films is heated at 430 C. for 3 hours in a forced draft oven under nitrogen. This converts it to a creaseable, amber film. It is confirmed by infrared examination that the poly(hydroxy amide) has been converted to the desired polybenzoxazole structure.

Another poly (hydroxyarnide) film is heated for 3 hours at 400 C. at a pressure less than 1 mm, likewise producing a creaseable, amber polybenzoxazole Still another film prepared as described above is dried for only minutes at 120 C. This is heated at 370 C. for 72 hours at less than 1 mm. pressure, producing a creaseable, amber film having an inherent viscosity of 0.59.

EXAMPLE 3 tration, washed and dried. The yield is 8.0 g. (91.5%) of polymer having an inherent viscosity in sulfuric acid of 2.07. A solution in N,N-dimethylf0rmamide is cast as films, which, on drying are clear and tough.

EXAMPLES 4-14 The corresponding polybenzoxazole film of good quality is produced by substituting each of the following aromatic diacid chlorides for isophthaloyl chloride in the procedure of Example 2: terephthaloyl chloride; biphenyl-3,3-dicarbonyl chloride; biphenyl-4,4'-dicarbonyl chloride; bis(3 chlorocarbonylphenyl)methane; 2,2 bis(3- chlorocarbonylphenyl)propane; naphthalene 2,6dicarbonyl chloride; naphthalene-1,8-dicarbonyl chloride; bis- (3 chlorocarbonylphenyl)sulfone; bis(3-chlorocarbonylphenyl)ketone; bis(4-chlorocarbonylphenyl)ketone; and bas(3-chlorocarbonylphenyl)sulfone.

EXAMPLES 15-25 L wherein R is an aromatic tetravalent radical selected from the group consisting of 1W lid i where Y is selected from the group consisting of alkylene, alkylidene, perfluoroalkylene, perfiuoroalkylidene, oxygen, sulfur, SO

where R is selected from the group consisting of hydrogen and lower alkyl; each ring nitrogen atom being attached directly to a carbon atom of a ring of the aromatic tetravalent radical ortho or peri to the carbon atom to which an oxygen atom is directly attached;

R' is selected from the group consisting of and where Z is selected from the group consisting of alkylene of 1 to 3 carbon atoms, oxygen, sulfur, and -SO and n is an integer sufficiently high to provide an inherent viscosity of at least 0.3 as measured at 30 C. as at 0.5 by weight solution in concentrated sulfuric acid.

(References on following page) 9 10 References Cited WILLIAM H. SHORT, Primary Examiner. UNITED STATES PATENTS L. L. LEE, Assistant Examiner. 2,904,537 9/1959 Brinker et a1. 260-78 c1. XR. 3,230,196 1/1966 Moyer 26 47 5 260-65, 78

3,332,907 6/1967 Angelo et a1. 260--47 

